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Growth of ZnO Thin Films on Silicon and Glass Substrate by Pulsed Laser Deposition a Thesis

Bikash Kumar Das

Thin films find a wide application in developing microelectronic devices, sensors, anti-reflective and protective coatings on advanced equipments, transparent electrodes etc. These make equipments versatile and more efficient. Various techniques are being devised to grow high quality thin films. One such advanced technique is the Pulsed Laser Deposition technique which comes under the category of Physical Vapour Deposition technique. In this technique the material to be deposited i.e. the target, is ablated using laser pulses resulting in the plasma formation. This plasma then interacts with the background gases supplied into the vacuum chamber. Finally it condenses on the object to be coated with the material i.e. the substrate, and nucleates to get deposited as a thin film. PLD is a simple, faster and economical technique. High quality films with desired crystalline structure can be grown using this technique. However a number of factors are involved which determine the film quality like pressure optimization, target composition and form, substrate temperature and laser pulse features. The project deals with deposition of zinc oxide on silicon and quartz substrates by PLD technique and to study the characteristic of the thin film by UV Visible spectroscopy. Zinc Oxide is considered to be a future material due to its multifunctional properties. It crystallizes in two structures viz. Hexagonal wurtzite and Cubic zinc blend. Its high conductivity and low thermal expansion leads to its wide application in ceramics. The striking feature of ZnO is that it is a wide direct band gap semiconductor with a band gap of 3.25eV which corresponds to energy in the UV range. It is a potential material to develop optoelectronic devices that would emit radiations in UV range. Besides the binding energy of excitons is 60 meV. This makes the excitons stable at room temperature (energy equivalent of which is 25 meV) and hence is an essential feature for lasing action. Developing ZnO oxide thin films facilitates research to develop ZnO optoelectronic devices. The project involves the study of the PLD technique and its various aspects like optimization conditions and film growth. A study has been made on the objective behind developing ZnO thin films. The study has inspired me to get involved in developing higher quality thin films for manufacturing optoelectronic devices made up of ZnO.